Dichromic printing by a portable label printing and applying machine or hand labeler and by a portable tagging machine is known. In one hand labeler, a pair of printing members are fixed to yokes which are pivotable up and down by actuation of a hand lever. A pair of independently rotatable arms are disposed in front of and at the back of those printing members. These arms independently and rotatably hold two inking rollers impregnated with different color inks. The rotating arms are pivotally connected to the frame of the hand labeler and are biased by a spring.
When the yokes are lowered by gripping of a hand lever, the front and rear printing members move downward and simultaneously push the front and rear inking rollers respectively frontward and rearward at the respective lower edges of the printing members. This rolls the inking rollers over the printing surfaces, which are formed at the lower edges of the front and rear printing members, and the printing surfaces are inked in different colors. The front inking roller is rolled over the printing surface of the front printing member, while the rear inking roller is rolled over the printing surface of the rear printing member. When the hand lever is further gripped, the yokes are lowered so that the printing surfaces abut the label, thus effecting dichromic printing.
However, the conventional ink supply mechanism has several drawbacks. Because the rotating arms holding the front and rear inking rollers are arranged at separate positions, the rotating arm for the rear inking roller must be attached to a center portion of the inside of the hand labeler. As a result, the hand labeler is so large in size that it cannot be handled with ease. Also, to enable replacement of an exhausted rear inking roller, more complicated means for removably attaching the rotating arm of that roller are required and this makes it difficult to handle the hand lever.
Moreover, the inking rollers are pushed into contact with the printing surfaces by the biasing force of a spring. This pushing force reduces as the spring is weakened due to its aging. The intensity of the inking declines so that the print on the label is not clear. This drawback becomes serious especially when the labels being printed are machine read, which requires precision printing.
Further, the printing surfaces should press more deeply into the surfaces of the inking rollers as the biasing force of the spring becomes weaker. But, because this does not occur, the ink which is trapped deep in the center portions of the inking rollers will not be pumped to the surfaces of the inking rollers by the pressure of the printing surfaces. As a result, only the ink that is stored near the surfaces of the inking rollers can be utilized. Thus, a set of inking rollers can imprint only a small number of labels, thereby making the label printing process uneconomical.
Finally, when the hand lever is squeezed rapidly, the inking rollers may jump and thereby avoid contacting the printing surfaces or only weakly contact these surfaces. This may prevent the label from being printed or may lead to shading of the inked imprints on the dichromically printed label.
Previous ink supply mechanisms are also shown in U.S. Application Ser. No. 716,934, filed Aug. 23, 1976 by the inventor hereof. But, these mechanisms generally have their inking rollers ink all of the printing surfaces. No effort is made to have each roller only ink a printing surface which prints one respective color.